chem is a command line tool and JavaScript code library that helps you to rapidly prototype 2D canvas-based video games for the Web. It automatically creates a sprite sheet for your assets and loads the assets at runtime, provides an API for drawing animated sprites in a canvas, and uses browserify to compile your code, allowing you to harness the power of code on npm. Everything from code to sprite sheets are compiled automatically when you save. It handles the main loop and frame skipping, provides an API for keyboard and mouse input, and bootstraps the resource loading process, optionally providing a basic loading progress bar.

MegaGlest is a real-time strategy game for up to eight players with a pseudo historic/fantasy theme and 3D graphics. Modding is easy thanks to simple XML formats and Blender export to the open G3D model format.

jMonkeyEngine is a game engine made for developers who want to create 3D games following modern technology standards. The framework is programmed entirely in Java, and aimed at wide accessibility and fast deployment to desktop, Web, and mobile platforms. It is not a visual “RPG Maker” or a drag-and-drop “FPS mod”. If you are comfortable writing Java code, you can rely on jMonkeyEngine as your next 3D game’s foundation.

Castle Game Engine is a cross-platform 3D game engine written in Object Pascal. It includes a flexible system of 3D objects, with out-of-the-box levels, items, intelligent creatures, and more. Rendering and processing of 3D models in X3D, VRML, Collada, and other formats is implemented. Many graphic effects are available, including shadows, bump mapping, shaders, mirrors, and screen effects.

RoseThorn is a cross-platform library for 2D and 3D games running on GNU/Linux (and possibly other Unix-like OSes) and Windows. Features include: hardware accelerated 2D and 3D rendering; Ogg and WAV Sound support with OpenAL; Lua scripting; BMP, JPEG, and PNG image loading and saving (from screenshots); easily created and modified user interfaces with XML and CSS, combined with Lua event handling; separate 2D and 3D libraries; support for multiple fonts in both TTF and bitmap formats; support for OBJ, 3DS, MD5, and RTM model formats; skeletal animation (a work in progress); support for UDP and TCP networking; thread and mutex support; a Simple Shader API; 2D animated sprites; and some basic cryptography support. There is simple event management, with key/mouse bindings easily customized from the in-game console, config file, command line, or GUI.

OpenXcom is a new engine for the old game UFO: Enemy Unknown (X-Com: UFO Defense in the USA),
a popular strategy videogame made by Mythos/Microprose in which you take control of the X-Com
organization to fight off the alien menace invading Earth.

Revised is a visual editor (or wizard/assistant/GUI) for Ren’Py, the visual-novel game editor. Ren'Py has a lot of capabilities, and Revised's purpose is not to allow everything that Ren'Py can do, just some of the basics. You can think of it as a step-by-step wizard to create the skeleton of a Ren'Py game.